In electronic restraining systems in vehicles, e.g. an inflatable air bag to restrain an occupant in the event of a crash, the system normally takes the form of one or more sensors which detect the deceleration of the vehicle and a control unit to monitor signals from each sensor and to supply an electrical signal to detonate electrically an inflation capsule to inflate the bag if the control unit determines that a crash condition has occurred. There is a requirement for the system to be able to trigger the safety function very rapidly in the event of a crash. However, it is also necessary that the restraining system should not be inadvertently actuated, for example in the event that a crash condition is incorrectly detected or if a short circuit occurs.
It is an object of the present invention to provide a detonation circuit for detonating an air bag which meets the above requirements and overcomes the aforementioned difficulties.